Battery packs are widely used that contains a plurality of primary or secondary battery cells, a circuit board, and a battery case encasing these components. When an electrolyte solution leaks from any of the battery cells, it can corrode the wiring of the circuit board, whereby there may occurs a conduction failure or short circuit. To prevent such corrosion and short circuits when leakage of the electrolyte solution occurs, a liquid-absorbing element containing an liquid absorbing agent capable of absorbing the electrolyte solution is arranged in the battery pack adjacent to or in the vicinity of the battery cell (Japanese Patent Application Laid-Open No. 2001-351588). Various polymer materials are used as the liquid absorbing agent, including adsorbents, gelling agents, and self-swelling agents. Among specific examples of the liquid absorbing agents described are polyacrylate-based water-absorbing resins, starch/graft copolymer-based water-absorbing resins, polyvinyl alcohol-based water-absorbing resins, polyacrylamide-based water-absorbing resins, isobutyrene-maleic acid copolymer-based water-absorbing resins, long chain alkyl acrylate crosslinked polymers, and polynorbornens.
One drawback of these liquid absorbing agents is that they cannot effectively absorb propylene carbonate, dimethyl carbonate and other carbonate-based solvents that are widely used in nonaqueous electrolyte battery packs, a type of batteries that have become increasingly used in recent years. Specifically, these solvents are used in nonaqueous electrolyte secondary cells that make lithium ion-based nonaqueous electrolyte secondary battery packs. Another drawback is that these adsorbents show little or no adhesion, so that they cannot be easily stuck to a nonwoven fabric support at room temperature and thus, require a thermal laminator. Furthermore, an adhesive layer must be arranged to apply the liquid absorbing agent to nonaqueous electrolyte secondary battery packs. As a result, the usable amount of the adhesive is decreased by an amount corresponding to the thickness of the adhesive layer.
The present invention addresses the above-described problems and to that end, it is an object of the present invention to provide a liquid absorbing sheet that shows adhesion and is capable of effectively absorbing the nonaqueous electrolyte solution used in nonaqueous electrolyte secondary cells that make nonaqueous electrolyte battery packs (in particular, lithium ion-based nonaqueous secondary battery packs). It is another object of the present invention to provide a battery pack equipped with an electrolyte-absorbing element made of such a liquid absorbing sheet.